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http://weblogs.asp.net/mhawley/archive/2004/05/11/129824.aspx

Large File Uploading in ASP.NET

I posted this to the ASP.NET forums back in November of 2002, and, too much of my dismay, still is an issue and people are still having problems figuring this out. I don't really know how many times I've helped people with this problem, and just recently I had to do the same. So, for my own personal reference (mainly), and to share the information, I decided to re-post it in my blog...

First the good...

To upload large files, and not receive the DNS Error or the page stopping while uploading, we found several settings between the machine.config and the web.config files that you need to modify. There are specifically 3 places, 2 of which can be overwritten in your web.config file.

In your web.config, add a line under your system.web <httpRuntime executionTimeout="54000" maxRequestLength="512000" /> where execution timeout is in seconds, and maxRequestLength is in KB. executionTimeout, is basically the amount of time a thread will continue to run, and accept data by IIS/.NET. maxRequestLength, is the total amount of data that can be sent through HTTP Post to the server. The default is 4MB (4096)...and is generally set low so that your server will not be overwhelmed by possible DoS attacks.

In your machine.config, modify responseDeadlockInterval to equal the same amount of time for executionTimeout. responseDeadlockInterval, is basically the amount of time that the Client's browser and Server will continue to communicate. Every several minutes or so, the server polls the client, asking if they have any more information to send, if they do not receive anything back after several times, then the server stops the current thread and all communication is stopped. This is the cause of the DNS Error you may see sometimes.

These 3 changes will allow you to successfully upload large files.

Now...the bad...

Memory deallocation is a major issue, that has no current solution. Whenever you upload files via HTTP Post, the file is stored in the memory of the aspnet_wp.exe process, and never deallocates completely (if your lucky a few MB gets released). One of the config settings for .NET processes, allows them to utilize 60% of physical memory on the server, at which point the process is recycled and all execution is stopped. Whenever a new upload is started, though, some memory is de-allocated, but not enough compared to memory that was used in prior uploads.

Microsoft is aware of this problem, and has assured us that it will be fixed with some upcoming releases of the .NET framework. Some solutions that they suggested to us, was to use Classic ASP, Third Party Components, or Custom Built ISAPI filters. Because of our solution we were using this in, we could do none of the three, so we topped the server out at 2GB of RAM. This has provided us with some breathing room if several people start uploading huge files, and gives us enough time to restart IIS if we start nearing 1.3GB of RAM being used by aspnet_wp.exe.